Effects of pruning with flower removal on the growth, starch reserves and secondary metabolites of a medicinal herb, Astragalus mongholicus

• 50 % pruning of Astragalus mongholicus improved concentration of root isoflavonoids. • Neither 50 % nor 25 % pruning with flower removal reduced root starch or biomass. • Pruning with flower removal can improve medicinal properties Radix Astragali. Astragalus membranaceus (Fisch.) Bge. var. mongholicus (Bge.) Hsiao is highly valued in traditional Chinese medicine, however, knowledge on the cultivation of this species for optimal root bioactive and biomass production is limited. This study investigated the effects of pruning intensities (0 [control], 25, and 50 %), where flower removal occurred concurrently with pruning, on biomass and starch content and secondary metabolite accumulation in the roots of A. mongholicus two and seven months after treatments were imposed. Shoot pruning at 50 %, combined with flower removal, significantly increased the accumulation of several isoflavonoids, particularly calycosin 7-O-β-D glucoside (31 %), calycosin isomers 1 (26 %) and 2 (27 %), pratensein isomer 1 (12 %), formononetin isomer 2 (21 %), and total isoflavonoids (19 %) compared to unpruned controls seven months after pruning. In contrast, the saponins, specifically astragaloside IV levels, remained unaffected by pruning with flower removal two- and seven-months post-pruning. Moreover, neither 25 % nor 50 % pruning with flower removal significantly influenced root biomass, total starch concentration and content. These findings indicate that pruning with flower removal can enhance the accumulation of valuable isoflavonoids without compromising root biomass or affecting optimal levels of astragaloside IV. Therefore, moderate (50 %) pruning, with flower removal, could optimise the medicinal quality of A. mongholicus roots.